[Backport 2.x] Add dynamic index and cluster setting for concurrent segment search

[jed326]

Add dynamic index and cluster setting for concurrent segment search (#7956)

• Add dynamic index and cluster setting for concurrent segment search
• Use feature flagged settings map

Related Issues

Resolves #7356

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)

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[jed326]

@reta Here is the backport PR for #7956. Thank you!

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/17403/
• CommitID: 7f36a28
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      2 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString

• URL: https://build.ci.opensearch.org/job/gradle-check/17406/
• CommitID: de25df2
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Merging #8034 (de25df2) into 2.x (55bb8f3) will decrease coverage by 0.04%.
The diff coverage is 91.42%.

@@             Coverage Diff              @@
##                2.x    #8034      +/-   ##
============================================
- Coverage     70.63%   70.59%   -0.04%     
+ Complexity    56661    56641      -20     
============================================
  Files          4695     4696       +1     
  Lines        268477   268499      +22     
  Branches      39699    39700       +1     
============================================
- Hits         189642   189554      -88     
- Misses        62558    62587      +29     
- Partials      16277    16358      +81     

Impacted Files	Coverage Δ
.../org/opensearch/search/internal/SearchContext.java	36.36% <0.00%> (-0.85%)	⬇️
...va/org/opensearch/search/DefaultSearchContext.java	78.57% <75.00%> (-0.12%)	⬇️
...rg/opensearch/common/settings/ClusterSettings.java	92.85% <100.00%> (+0.35%)	⬆️
...pensearch/common/settings/IndexScopedSettings.java	100.00% <100.00%> (ø)
.../main/java/org/opensearch/index/IndexSettings.java	86.95% <100.00%> (+0.06%)	⬆️
.../main/java/org/opensearch/search/SearchModule.java	97.53% <100.00%> (-0.02%)	⬇️
...main/java/org/opensearch/search/SearchService.java	72.39% <100.00%> (+0.79%)	⬆️
...rch/search/query/ConcurrentQueryPhaseSearcher.java	75.00% <100.00%> (+5.30%)	⬆️
...search/search/query/QueryPhaseSearcherWrapper.java	100.00% <100.00%> (ø)

... and 482 files with indirect coverage changes